Sen. Barbara Boxer on Wednesday sought to shift the heated debate over Keystone XL from climate change to the public health effects of processing the oil sands that the pipeline would transport.

Boxer, D-Calif., and Sen. Sheldon Whitehouse, D-R.I., sent a letter to Secretary of State John Kerry asking for a“comprehensive human health impacts study” analyzing the respiratory ailments, cancer and other illnesses that could be tied to harvesting and refining the dense hydrocarbon bitumen in Alberta’s oil sands.

“The health impacts of tar sands oil are being ignored,” Boxer said at a Capitol Hill news conference where she was flanked by activists and doctors.“This press conference is about waking up Americans that more tar sands coming into this country is a danger to the health of our people, all along the way, from the extraction to the transport, to the refining.”

The move represents a new strategy in opponents’ fight against the oil pipeline, as the State Department moves from environmental studies of the project to formally weighing whether the border-crossing project is in the national interest, a determination that wraps in energy security, economic factors and other issues.

Although President Barack Obama has said the project’s contribution to climate change will be a major factor in his final decision, pipeline foes acknowledged the“human costs” of the project could be more compelling.

“The public health impacts are something that average people can really relate to, because they know cancer is the second-leading cause of death in this country, heart disease is one, and all of this filthy air contributes to both of those,” Boxer said.

Hilton Kelley, founder of the Community In-Power and Development Association in the southeast Texas city of Port Arthur, said the diluted bitumen that would be transported by Keystone XL can devastate Gulf Coast communities living in the shadows of the refineries that process it.

“If this tar sand material is processed in the cities of Port Arthur, Texas, and Houston, there will be a serious increase in various toxic materials in the air that people must breathe in southeast Texas,” Kelley said at the news conference.“Enough is enough. We do not need, nor do we want tar sands material in our communities. It’s time for the onslaught to end.”

Boxer and Whitehouse noted that refinery communities have higher levels of air pollutants, and said that people living near the facilities suffer from“higher rates of the types of cancers linked to these toxic chemicals, including leukemia and non-Hodgkin’s lymphoma.” They also highlighted potential dangers from storage of petroleum coke, a waste byproduct generated in processing of heavy oils.

Health effects from pet coke are unclear. At least one government agency in Michigan earlier this month documented“no observed carcinogenic, reproductive or developmental effects” from the product.

But Boxer and Whitehouse said the risks are too great.

“Putting more Americans at risk for asthma, cancer and other serious health impacts is not in our national interest,” Boxer and Whitehouse said in their letter to Kerry.

“Clearly, much more needs to be done before any final decision on the Keystone XL pipeline is made.”

“Nothing less than the health of our families is at stake,” they added.

Whitehouse said the final decision on whether to permit the project should“be made by this country with our eyes wide open to the health effects, to the climate effects, and (without taking) as gospel parts of a report that was clearly written by a consultant with a significant affinity for the industry that wants the Keystone pipeline to proceed.”

Keystone XL supporters said the tactic showed environmentalists are desperate to find a new approach against TransCanada Corp.’s project, after a State Department environmental analysis concluded the bitumen in Canada’s oil sands will be produced with or without the pipeline, so its approval wouldn’t add significantly to greenhouse gas emissions tied to the production.

“Keystone XL clearly passes President Obama’s climate test, so opponents are scrambling to find any other way to slow down the process,” said Katie Brown, a spokeswoman for Oil Sands Fact Check.“But their tactics won’t work. An overwhelming majority of Americans, from all sides of the political spectrum, want the jobs, economic prosperity and energy security the pipeline would bring.”

Sen. John Barrasso, R-Wyo., also took a jab at the approach taken by Boxer and Whitehouse.

“If they’re worried about health,” he said in a tweet,“let’s study the impact of unemployment for out-of-work American who would welcome Keystone XL jobs.”

Boxer, the head of the Senate Environment and Public Works Committee, vowed to“use whatever tools I have at my disposal to get out the truth about tar sands.” She did not immediately commit to holding hearings on the issue but said that was a possibility.